1. Field of the Invention
The invention relates to a carrier device which suctions and secures a film of organic compound which is used for flexible printed boards or the like, and an easily deformable workpiece of thin metal foil or the like which is used for the magnetic head of a hard disk (hereinafter, together generally called a xe2x80x9cflexible boardxe2x80x9d). The invention relates especially to an arrangement of a vacuum suction groove by which the flexible board is suctioned and secured on the carrier without being deformed.
2. Description of Related Art
An exposure device by which a pattern, such as a circuit or the like, is exposed in a semiconductor wafer, conventionally, has a carrier (hereinafter, called an exposure carrier) which can hold the semiconductor wafer securely. The reason for this is that it is necessary to secure the semiconductor wafer in the exposure carrier to prevent the following during transport of the semiconductor wafer to an exposure position and in the placement of the semiconductor wafer on the exposure carrier:
the semiconductor wafer from diverging from the exposure position of the exposure carrier, and
a position deviation arising in the semiconductor wafer during exposure as a result of vibration or the like and thus faulty exposure occurring.
As the means for securing the semiconductor wafer in the exposure carrier, generally a vacuum suction process is used in which the pressure in the space between the workpiece, such as the semiconductor wafer or the like, and the carrier is reduced so that the workpiece is drawn onto the carrier by the pressure difference relative to atmospheric pressure, and thus, the workpiece is secured on the carrier.
In an exposure carrier using the vacuum suction process (hereinafter called a vacuum suction carrier), the carrier surface on which the semiconductor wafer is placed is provided with holes, grooves, and the like which are used to form a negative pressure space between the semiconductor wafer and the vacuum suction carrier, and to which a vacuum system is attached which is used to supply the vacuum.
Japanese patent disclosure document HEI 5-218183 discloses a carrier in which the carrier surface on which the semiconductor wafer is placed is provided with vacuum suction openings. Furthermore, Japanese patent disclosure document HEI 6-333799 discloses a carrier in which in the center of the carrier surface on which the semiconductor wafer is placed, there is a vacuum suction opening around which several vacuum suction grooves are concentrically arranged relative to one another, and in which furthermore, proceeding from the above described vacuum suction opening, connecting grooves are radially arranged in order to connect the above described vacuum suction opening to the above described vacuum suction grooves.
Recently, there has been a demand for the formation of a fine circuit pattern not only in a semiconductor wafer, but also in a film of organic compounds with a thickness of roughly 20 to 150 microns, and in an easily deformable workpiece, such as a thin metal foil or the like, i.e., in a flexible board. As the device for forming the circuit pattern, an exposure device with the above described vacuum suction carrier is being used more and more often. However, when using the above described exposure device for a flexible board or the like, there are also cases in which the following disadvantage arises:
FIG. 6 schematically shows a state in which a flexible board is held securely by a carrier which is provided with several vacuum suction openings. FIG. 7 schematically shows a state in which a flexible board is securely held by a carrier which has several rectangular vacuum suction grooves which are located concentrically around a vacuum suction opening, and connecting grooves which connect the vacuum suction opening and the vacuum suction grooves to one another.
In the case in which the flexible board 4, for example, a strip workpiece 4a, with a great length is held by the vacuum suction carrier 1 shown in FIGS. 6 and 7, between the vacuum suction openings 2a, or between the vacuum suction grooves 2b; air accumulations form, which result in cases in which the strip workpiece 4a is deformed such that it partially projects.
If, in the state in which these air accumulations 3 have formed, for example, in a projection exposure device, a projection lens projects a circuit pattern which has been formed in the mask onto the strip workpiece 4a, the sites of the strip workpiece 4a at which the air accumulations 3 have formed are located at positions which diverge from the imaging position of the mask pattern. The projection image of the mask pattern therefore becomes blurry, by which faulty image resolution, variation of the dimensions of the wiring pattern and the like arise. Therefore, there are cases in which faulty products result.
In the case of an exposure device in which alignment marks which are recorded on the mask and workpiece are determined and processed using an image processing device and in which thus the mask is positioned to the workpiece, workpiece mark images which are taken into the image processing device are deformed or they become blurry when the points provided with the workpiece alignment marks (workpiece marks) project in the manner described above. The image processing device cannot detect the workpiece marks. Therefore, the workpiece mark images can no longer be determined, and the mask can no longer be positioned relative to the workpiece.
The above described air accumulations are presumably formed by the following mechanism.
When the flexible board, for example, the strip workpiece 4a, is placed on a carrier surface 1a, not all the air between the carrier surface 1a and the strip workpiece 4a can be forced out since the strip workpiece 4a is thin and can be easily deformed. The strip workpiece 4a is therefore placed on the carrier surface 1a in the state in which it contains little air. When the vacuum suction openings 2a or vacuum suction grooves 2b are supplied with a vacuum, at the sites of the strip workpiece 4a which are located on the vacuum suction openings 2a or vacuum suction grooves 2b, a pressure difference relative to atmospheric pressure is formed by which the strip workpiece 4a is drawn against the carrier surface 1a. If, in doing so, air remains in the areas which are surrounded by the openings 2a or the grooves 2b, the air is enclosed by the deformation of the strip workpiece 4a and occurs as an air accumulation 3 (FIG. 8(a) and 8(b)).
The invention was devised to eliminate the above described defect in the prior art. Thus, a primary object of the invention is to devise a carrier device in which no air can accumulate between the flexible board and the carrier surface when the flexible board is held securely by vacuum suction on the carrier surface.
The inventor has stated that numerous air accumulations form between the flexible board and the carrier surface in the areas which are surrounded by the vacuum suction openings or the vacuum suction grooves which are located on the carrier surface. Based on this statement he has considered the following.
Specifically, if a vacuum is supplied to the vacuum suction openings and or the vacuum suction grooves, so that the flexible board is held by the carrier surface, the flexible board presses the air between the carrier surface and the flexible board onto the edge of the flexible board and it is suctioned against the carrier surface and secured. If, in doing so, there are areas on the carrier surface which are surrounded by vacuum suction openings or vacuum suction grooves, the flexible board is suctioned by the vacuum suction openings or vacuum suction grooves before the air between the carrier surface and the flexible board completely disappears. As a result the air remaining between the carrier surface and the flexible board cannot escape and an air accumulation is formed.
Based on the above described consideration, the inventor found that the formation of air accumulations can be prevented by placing vacuum suction openings or vacuum suction grooves on the carrier surface such that no area is formed which is surrounded by the vacuum suction openings or vacuum suction grooves. The inventor devised the invention based on this finding.
The above object is achieved, according to the invention, in a carrier device for securing the flexible board by vacuum suction in that the carrier surface of the carrier device on which the above described flexible board is placed is provided with an opening for supplying a vacuum and with several grooves which extend radially from the opening, and that the grooves are connected to one another only at the above described opening.
The above described arrangement prevents an area from being formed on the carrier surface which is surrounded by the vacuum suction openings or grooves (on all sides). The air remaining between the carrier surface and the flexible board is therefore gradually forced to the outside proceeding from the vacuum supply opening, i.e., in the direction toward the edge of the flexible board when the flexible board is securely held by the carrier surface by vacuum suction.